1. Field of the Invention
The invention relates to a pipe with a rib, and a method for manufacturing the pipe with a rib.
2. Description of Related Art
In Japanese Patent Application Publication No. 2012-61518 (JP 2012-61518 A), a free casting method is proposed as an up-drawing continuous casting method that does not require a mold. As described in JP 2012-61518 A, after a starter is immersed into a surface of molten metal (or a molten metal surface), the starter is drawn up, and then, the molten metal is also drawn out following the starter by a surface film and surface tension of the molten metal. Here, the molten metal is drawn out through a shape defining member placed near the molten metal surface, and then cooled. This way, continuous casting of a casting having a desired sectional shape is achieved.
In an usual continuous casting method, a shape in a longitudinal direction, as well as a sectional shape, are defined by a mold. In a continuous casting method in particular, solidified metal (or a casting) needs to pass through inside of a mold. Therefore, a casting that has been cast has a shape that extends linearly in a longitudinal direction. On the contrary, in a free casting method, a shape defining member defines only a sectional shape of a casting, and does not define a shape in a longitudinal direction. Since the shape defining member is able to move in a direction parallel to a molten metal surface (or a horizontal direction), castings with various longitudinal shapes are obtained. For example, JP 2012-61518 A describes a hollow casting (or a pipe) formed into a zigzag or helical shape, instead of a linear shape, in a longitudinal direction.
The inventors have found out the followings. With conventional methods including extrusion molding, press forming, welding, cutting, metal mold casting, and so on, it has been extremely difficult to manufacture a pipe that has a rib inside and is non-linearly shaped.